Raspberry Pi Power supply confirmed as 5V micro USB

There has been a lot of speculation about the power supply design for the production Raspberry Pi devices. The alpha boards use a pair of switch-mode power supplies to generate 5V and 3V3 rails from a 6-20V input on a coaxial jack, and LDOs to generate the low-current 2V5 and 1V8 rails for the analog TV DAC and various I/O functions. This is a flexible and power-efficient design, but suffers from two drawbacks:

Expense. The two switch-mode parts and their accompanying inductors add roughly $2 to the cost of the device.

No support for 5V input. To correctly generate the 5V rail, more than 5V has to be presented at the input.

After a lot of experiments and spreadsheet work, we finally settled on an LDO-only power supply design, with a fixed 5V input, and the 1V2 core voltage generated directly from the input using the internal switch-mode supply on the BCM2835 die. We have chosen a 5V micro-USB jack to supply power to the board, for two reasons:

Ubiquity. Micro USB has been chosen as the GSMA’s Universal Charging Solution, so we expect AC adapters with this connector to be cheap and plentiful.

Voltage assurance. Unlike coaxial jacks, we know that we’ll be receiving 5V over this connector, which we can pass on unregulated to HDMI and USB devices.

Model B owners using networking and high-current USB peripherals will require a supply which can source 700mA (many phone chargers meet this requirement). Model A owners with powered USB devices will be able to get away with a much lower current capacity (300mA feels like a reasonable safety margin).

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